Dielectric properties and other physical properties of low-acyl gellan gel as relevant to microwave assisted pasteurization process

Abstract

Various model foods were needed as chemical marker carriers for the heating pattern determination in developing microwave heating processes. It is essential that these model foods have matching physical properties with the food products that will be microwave processed, such as meat, vegetables, pasta, etc. In this study, the physical properties of low acyl gellan gel were investigated to evaluate its suitability to be used as a possible model food for the development of single mode 915MHz microwave assisted pasteurization processes. These physical properties included the dielectric properties, gel strength and water holding capacities. In order to adjust the dielectric constant and loss factor, various amounts of sucrose (0, 0.1, 0.3 and 0.5g/mL (solution)) and salt (0, 100, 200, and 300mM) were added to 1% gellan gel (with 6mM Ca2+ addition). Results showed that sucrose and salt addition were effective for the adjustment of the dielectric constants and loss factor of gellan gels, respectively. Regression equations were developed to predict the relationship between the dielectric properties of gellan gel with sucrose content, salt content, and temperature (22–100°C) at 915MHz, and thus can be used to determine the formulation of a gellan gel model food to match the dielectric properties of a certain food that will be processed. The gellan gels with sucrose content of 0, 0.1 and 0.3g/mL (solution) showed relatively high gel strength for post microwave process handling. However, the addition of 0.5g/mL (solution) sucrose significantly decreased the gel strength, resulting in highly deformable gels. The water holding capacities of all the gels increased with increasing sucrose content, while the effect of salt was not consistent.